| O'Brien (Barony) |
Murrough O'Brien - Wed 21st Oct 1654
|
3 July 1855 |
- |
| of Offaly (Earldom) |
James Fitzgerald - Thu 19th Mar 1761
|
- |
- |
| Ogle (Viscountcy) |
William Ogle - Sat 23rd Dec 1645
|
14 July 1682 |
- |
| O'Grady (Barony) |
Standish O'Grady - Thu 6th Jan 1831
|
15 October 1955 |
- |
| O'Neill (Earldom) |
Charles Henry O'Neill - Thu 28th Aug 1800
|
25 March 1841 |
- |
| O'Neill (Viscountcy) |
John O'Neill - Sat 3rd Oct 1795
|
12 February 1855 |
- |
| O'Neill (Barony) |
John O'Neill - Fri 25th Oct 1793
|
12 February 1855 |
- |
| Ongley (Barony) |
Robert Henley Ongley - Tue 30th Jul 1776
|
21 January 1877 |
- |
| Oranmore and Browne (Barony) |
Dominick Browne - Wed 4th May 1836
|
- |
- |
| Oriel (Barony) |
Margaretta Amelia Foster - Sat 5th Jun 1790
|
- |
- |
| of Ormond (Dukedom) |
James Butler - Wed 30th Mar 1661
|
17 December 1758 |
- |
| of Ormond (Marquessate) |
James Butler - Sat 30th Aug 1642
|
17 December 1758 |
- |
| of Ormond (Marquessate) |
Walter Butler - Fri 12th Jan 1816
|
10 August 1820 |
- |
| of Ormond (Marquessate) |
James Wandesford Butler - Wed 5th Oct 1825
|
25 October 1997 |
- |
| of Orrery (Earldom) |
Roger Boyle - Sun 5th Sep 1660
|
- |
- |
| Orwell (Viscountcy) |
Francis Vernon - Sun 21st Jul 1776
|
15 October 1783 |
- |
| Orwell (Barony) |
Francis Vernon - Wed 7th Apr 1762
|
15 October 1783 |
- |
| of Ossory (Earldom) |
Piers Butler - Sun 23rd Feb 1528
|
- |
- |
| Oxmantown (Barony) |
Richard Parsons - Wed 2nd Jul 1681
|
27 August 1764 |
- |
| Oxmantown (Viscountcy) |
Laurence Harman Harman - Fri 2nd Oct 1795
|
20 April 1807 |
- |